Fixed rounding issue on scrollbar rasterization.

cc/test/fake_painted_scrollbar_layer.cc

Index: cc/test/fake_painted_scrollbar_layer.cc
diff --git a/cc/test/fake_painted_scrollbar_layer.cc b/cc/test/fake_painted_scrollbar_layer.cc
index 72ef420a89c26f4320a2cbdcef564e3fe57ffb98..81d85bb750f66db2380626745dc3f2b85f6b7a08 100644
--- a/cc/test/fake_painted_scrollbar_layer.cc
+++ b/cc/test/fake_painted_scrollbar_layer.cc
@@ -13,9 +13,10 @@ namespace cc {
 scoped_refptr<FakePaintedScrollbarLayer> FakePaintedScrollbarLayer::Create(
     bool paint_during_update,
     bool has_thumb,
-    int scrolling_layer_id) {
-  FakeScrollbar* fake_scrollbar = new FakeScrollbar(
-      paint_during_update, has_thumb, false);
+    int scrolling_layer_id,
+    FakeScrollbar* fake_scrollbar) {
+  if (!fake_scrollbar)
+    fake_scrollbar = new FakeScrollbar(paint_during_update, has_thumb, false);
   return make_scoped_refptr(new FakePaintedScrollbarLayer(
       fake_scrollbar, scrolling_layer_id));
 }